Field of the Invention
The present invention relates to a heat treatment apparatus that irradiates a thin-plate precision electronic substrate (hereinafter, merely referred to as a “substrate”) such as a semiconductor wafer with light to heat the substrate.
Description of Background Art
In the manufacturing process of a semiconductor device, the introduction of impurities is an essential step for forming pn junctions in a semiconductor wafer. Currently, impurities are typically introduced by ion implantation and subsequent annealing. Ion implantation is a technique for physically implanting impurities by ionizing impurity elements such as boron (B), arsenic (As), and phosphorus (P) and causing the impurity elements to collide with a semiconductor wafer at a high acceleration voltage. The implanted impurities are activated by annealing. If, at this time, annealing time is approximately several seconds or more, the implanted impurities are deeply diffused by heat. As a result, a junction depth may become deeper than necessary, possibly interfering with excellent formation of a device.
Thus, flash lamp annealing (FLA) has recently been receiving attention as an annealing technique for heating a semiconductor wafer in an extremely short time. The flash lamp annealing is a heat treatment technique for raising the temperature of only a surface of the semiconductor wafer implanted with impurities in an extremely short time (a few milliseconds or less) by irradiating the surface of the semiconductor wafer with flash light using xenon flash lamps (hereinafter, the term “flash lamps” used means xenon flash lamps).
The xenon flash lamps have a spectral distribution of radiation ranging from ultraviolet regions to near-infrared regions. A wavelength of light emitted from the xenon flash lamps is shorter than that of light emitted from conventional halogen lamps and substantially coincides with a fundamental absorption band of a silicon semiconductor wafer. Thus, the temperature of the semiconductor wafer can be rapidly increased with a small amount of transmitted light when the semiconductor wafer is irradiated with flash light from the xenon flash lamps. It has been determined that the irradiation with flash light in an extremely short time of a few milliseconds or less can selectively raise the temperature of only near the surface of the semiconductor wafer. Accordingly, such a temperature rise in an extremely short time using the xenon flash lamps allows impurities to be only activated without being deeply diffused.
US2009/0175605 discloses a heating treatment apparatus that includes such xenon flash lamps and has a technique for performing flash heating on a semiconductor wafer supported by a plurality of bumps (support pins) that are in point-contact with the semiconductor wafer and formed on a top surface of a quartz susceptor. The apparatus disclosed in US2009/0175605 irradiates a bottom surface of the semiconductor wafer placed on the susceptor with light emitted from halogen lamps to preheat the semiconductor wafer, and subsequently performs flash heating by irradiating a front surface of the wafer with flash light emitted from the flash lamps.
As disclosed in US2009/0175605, in the case where the semiconductor wafer is supported by the plurality of support pins in point-contact therewith, heat is transmitted between the semiconductor wafer and the support pins at the contact portions. In preheating by the irradiation with the light from the halogen lamps, quartz hardly absorbs the light. Thus, the semiconductor wafer is heated to a temperature higher than that of the quartz susceptor, causing heat to be transmitted from the semiconductor wafer to the support pins. As a result, the vicinities of the contact portions in the semiconductor wafer plane in contact with the plurality of support pins are relatively at a temperature lower than that of the other regions.
For this reason, Japanese Patent Application Laid-Open No. 2015-18909 proposes that a laser beam emitted from a laser light source is reflected by a reflection portion to be introduced to a support pin, and the vicinity of the contact portion between the support pin and the semiconductor wafer in which a temperature tends to drop is heated in an auxiliary manner to prevent the relative drop of the temperature at the portion.
However, for the apparatus disclosed in Japanese Patent Application Laid-Open No. 2015-18909, a plurality of (the same number as the support pins) laser light sources need to be disposed in the chamber. The chamber needs to have a capacity at a minimum in terms of suppressing an amount of atmospheric gas consumed, and thus many laser light sources are hardly disposed in the chamber. It is also preferred that a minimum of devices, which may become sources of contamination, needs to be disposed in the chamber housing the semiconductor wafer.